Control method and device for optical filter

A tracking control device for an optical filter including first and second optical filter units cascaded, each having an input and first and second outputs, said first output of said first optical filter unit being connected to said input of said second optical filter unit and light having a first wavelength is supplied to said input of said first optical filter unit, said tracking control device comprising:

• a first converter converting first light output from said second output of said first optical filter unit into a first electrical signal having a level corresponding to the power of said first light;
• a second converter converting second light output from said second output of said second optical filter unit into a second electrical signal having a level corresponding to the power of said second light;
• a circuit weighting said first and second electrical signals according to losses in said first and second optical filter units;
• a circuit adding said weighted first electrical signal and said weighted second electrical signal;
• and
• a circuit controlling said first and second optical filter units so as to make a center wavelength in a transmission characteristic of each of said first and second optical filter units coincide with said first wavelength according to said added signals.